Soap tablet production

ABSTRACT

A PROCESS FOR THE MANUFACTURE OF SOAP TABLETS INCORPORATING MINOR AMOUNTS OF ALKALINE EARTH METAL ALKYL ARYL SULPHONATES, IN WHICH PROCESS THE TABLETS ARE SUPERFATTED BY THE ADDITION TO A SOAP BASE OF A MINOR AMOUNT OF FREE ALKYL ARYL SULLPHONIC ACID, IS DISCLOSED. PREFERABLY, THE ALKALINE EARTH METAL ALKYL ARYL SULPHONATES ARE FORMED IN SITU IN A SOAP BASE BY THE ADDITION TO THE SOAP BASE OF AN ANHYDROUS ALKALINE EARTH METAL OXIDE-SULPHONIC ACID SLURRY, THE TABLETS BEING FORMED SUBSEQUENTLY FROM THE SOAP BASE.

United States Patent 3,723,329 SOAP TABLET PRODUCTION Elfed Huw Evans, Mold, Wales, assignor to Lever Brothers Company, New York, N.Y.

No Drawing. Filed Nov. 2, 1970, Ser. No. 86,373 Claims priority, application Great Britain, Nov. 7, 1969, 54,624/69, 54,625/69 Int. Cl. C11d 9/32 U.S. Cl. 252--121 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to the production of soap tablets, and in particular of soap tablets adapted for personal washing, commonly called toilet tablets, which incorporate minor proportions of synthetic detergent active compounds having beneficial effects on the lathering properties of the soap tablets.

Conventional soap tablets comprise essentially mixtures of alkali-metal soaps derived from tallow-class fats and nut oils. In general, the lathering properties of nut oil soaps are superior to those of tallow soaps, particularly as regards lather volume, but as nut oils are more expensive than tallows it is generally not practicable or desirable to make soap tablets exclusively from nut oil soaps. It has been suggested to incorporated into a soap tablet a suitable amount of an alkaline earth metal alkyl aryl sulphonate detergent active compound to improve the lathering properties of the soap tablet.

According to the present invention it has been found that if a substantially anhydrous mixture of an alkaline earth metal oxide and an alkyl aryl sulphonic acid is added to a soap base, the production of these soap tablets is considerably facilitated.

By the present invention it has also been found that if a soap tablet containing a minor proportion of an alkaline earth metal alkyl aryl sulphonate detergent active compound contains in addition a minor proportion of free fatty acid liberated from the soap during the production of the toilet tablet by the use of free alkyl aryl sulphonic acid, the enhanced lather volume characteristics outlined above are maintained and also the mushing properties of the resultant soap tablet are considerably improved.

The incorporation of free fatty acid in a soap tablet of the invention can conveniently be achieved by using an excess of alkyl aryl sulphonic acid in a substantially anhydrous mixture of an alkaline earth metal oxide and an alkyl aryl sulphonic acid used to prepare the soap tablet.

Hitherto, an alkaline earth metal alkyl aryl sulphonate detergent active compound has been incorporated into an aqueous soap base either by the addition of an aqueous paste of the sulphonate to a sodium soap base, or by 3,723,329 Patented Mar. 27, 1973 the addition of an aqueous paste of a sodium alkyl aryl sulphonate detergent active compound to a soap base comprising a mixture of sodium and alkaline earth metal soaps. These processes have necessarily involved the subsequent crutching and drying of the resultant mixture before the familiar techniques of soap tablet production, such as milling and stamping, can be applied. It has been found in practice that considerable heat energy is required in order to dry such a mixture of soap and synthetic detergent active to an acceptable low water content. The soap bases utilised in these processes generally contain from 30 to 40% by weight of water and the sulphonate pastes generally contain up to 50% by weight of Water, whereas a soap mixture to be processed into tablet form should preferably have a water content of about 743% by weight.

The invention provides a process whereby an aqueous soap base, preferably dried to a water content of from 7 to 13% by weight, is intimately mixed with a substantially anhydrous slurry comprising essentially a mixture of one or more alkaline earth metal oxides together with one or more alkyl aryl sulphonic acids, there being present in the slurry at least about 2 parts by weight of alkyl aryl sulphonic acid per part by weight of alkaline earth metal oxide, the alkyl groups of which contain from 8-22 carbon atoms, the soap base and slurry being subsequently formed into tablets.

-In a preferred embodiment of the above process, the substantially anhydrous slurry comprises one or more alkaline earth metal oxides and one or more alkyl aryl sulphonic acids, the alkyl aryl sulphonic acid or acids being present in an amount, exceeding the amount stoichiometrically equivalent to the amount of alkaline earth metal oxide, from about 1 to about 10% by weight of the finished tablets.

The invention also provides a process in which free alkyl aryl sulphonic acid is used to liberate free fatty acids from soap and in which process the soap is used in the production of a soap tablet comprising soap and an alkaline earth metal alkyl aryl sulphonate detergent active compound, the alkyl aryl sulphonic acid being used in an amount from about 1 to about 20% by weight of the finished tablet.

It will be appreciated that a free alkyl aryl sulphonic acid, being a stronger acid than a fatty acid, will displace fatty acid from soap with which it is mixed. Thus a finished soap tablet is unlikely to contain free sulphonic acid, but will, if excess free sulphonic acid is used in the preparation of the tablet, contain free fatty acid and the corresponding salt of the sulphonic acid.

In a preferred embodiment of the invention, an alkaline earth metal oxide and alkyl aryl sulphonic acid mixture is mixed with a previously-dried soap base, the residual water in the soap base being suificient to permit in situ formation of the required alkaline earth metal alkyl aryl sulphonate detergent active compound and the resulting mixture being suitable for immediate formation into tablets. Previously it has been considered essential that any such soaps and alkaline earth metal sulphonates should be preformed before being mixed, as their production in situ would result in the formation of considerable amounts of insoluble alkaline earth metal soaps, and that in consequence deleterious properties would be imparted to the toilet tablets derived from such a mixture. However, in a process in accordance with the present invention, in which the mixed alkaline earth metal oxide and sulphonic acid are added as a substantially anhydrous slurry to a preformed alkali-metal soap base, no such deterioration of the desirable properties of the subsequently formed soap tablets is observed.

The invention icludes soap tablets prepared by any of the above processes.

The alkaline earth metal oxides referred to above are the oxides of the elements in Group II-A of the Mendeleev Periodic Classification. The preferred alkaline earth metals are magnesium, and, less preferably, calcium.

Alkyl aryl sulphonic acids suitable for use in accordance with the invention are well-known commercially available materials. -In general they are alkyl benzene sulphonic acids, the alkyl groups of which contain from 8 to 22 carbon atoms, for example p-octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, eicosyl and doco'syl benzene sulphonic acids. The alkyl groups may be linear or branched the former being commonly derived from parafiins and the latter from synthetic materials, particularly low molecular weight homopolymers of propylene, for example tetrapropylene and pentapropylene. Preferably, however, linear alkyl benzene sulphonic acids are used as these compounds are biodegradable. Mixed alkyl aryl sulphonic acids may be used if desired. The amount of sulphonic acid used to liberate fatty acid from soap during a process of the invention should preferably be from about 1 to about 20% by weight (calculated as though the sulphonic acid remains as free sulphonic acid in the finished soap tablets) of the soap tablets.

The amounts of alkaline earth metal alkyl aryl sulphonates employed in soap tablets produced in accordance with the invention may be varied according to the desired properties of the tablets. Preferably, however, the amount is within the range of from about 5 to about 20% and particularly preferably from about 5 to about by weight.

The soaps to be employed in the present invention are water soluble salts of higher fatty acids, particularly the alkali metal salts, for example the sodium and potassium salts, thereof. Such higher fatty acids in general have chain lengths comprising from 8 to carbon atoms, and predominantly from 10 to 18 carbon atoms. The soaps are conventionally prepared by the saponification with alkaline materials of mixtures of tallow-class fats and nut oils. Examples of tallow-class fats include beef tallow, mutton tallow, lard, palm oil and some vegetable butters, and, if desired, hardened tallow class fats may also be employed. Examples of nut oils are palm kernel oil and coconut oil. Whereas the fatty acids derived from tallow-class fats contain major proportions of C and C fatty acids, the fatty acids derived from nut oils are predominantly C -C fatty acids. Alternatively, synthetic fatty acids may be used.

In addition to the essential soaps and the alkaline earth metal alkyl aryl sulphonates, soap tablets produced in accordance with the invention may incorporate conventional additives including, for example, perfumes, fillers, colourants, germicides and preservatives.

In a preferred process of the present invention, a substantially anhydrous alkaline earth metal oxide, or mixture of such oxides, is finely dispersed in a substantially anhydrous alkyl aryl sulphonic acid, or mixture of such acids, preferably in amounts such that there is at least about 2 moles of acid per mole of oxide. A slight excess of oxide can be used without the deterioration of the desirable properties of the finished soap tablets, provided the amount of excess oxide does not exceed about 1% by weight of the soap tablets. The resulting slurry is then added to a preformed alkali-metal soap base, preferably after the soap base has been dried to a water content of from about 7 to about 13%, and more preferabl from 8 to 10%, by weight.

It has been found particularly advantageous to add the slurry to the soap base in a soap drier at a late stage of the soap base drying operation. Alternatively, the slurry can be injected into the hot liquid soap base as it leaves the soap drier, or the slurry can be milled with dried soap base chips. In a less preferred process in accordance with the invention, the slurry is added to the soap base in a soap drier at the start of the drying openation.

After the addition of the slurry to the soap base, thorough mixing is required in order that the oxide and acid may react completely and that the resulting alkaline earth metal sulphonate may be dispersed homogeneously throughout the soap base. Subsequent plodding and formation into tablets of the. mixture can be achieved using any of the conventional techniques for this purpose.

In a process according to the invention in which an alkyl aryl sulphonic acid is used to liberate free fatty acids from soap, the alkyl aryl sulphonic acid may be added to a soap base before, during, or after the drying of the soap base.

The following examples, in which all parts and percentages are by weight, are presented to illustrate the invention.

EXAMPLE 1 A 63% total fatty matter sodium soap base was obtained by the saponification by caustic soda of a 70/30 mixture of tallow-class fats and coconut oil, and this was dried to a water content of 8%. A slurry was prepared comprising powdered anhydrous magnesium oxide and anhydrous dodecyl benzene sulphonic acid (sulphouated DOB 055, obtained from Shell) in a 1:2 molar ratio, the oxide being finely dispersed throughout the sulphonic acid by passage of the slurry through a colloid mill. As the hot liquid soap base was removed from the drier it was injected with the slurry, passed through an in-line mixer, and then cooled. After the addition of other additives, such as perfumes and colourants, the soap-sulphonate mixture was plodded and stamped into tablets using conventional apparatus.

The soap tablets produced by the above method had the following constitution.

Percent Sodium tallow soap 56 Sodium coconut soap 24 Magnesium dodecyl benzene sulphonate l0 Perfumes, colourants, etc. 2

Water to These soap tablets possessed excellent lathering properties, particularly in regard to the volume of the lather they produced.

EXAMPLE 2 Soap tablets having the following constitution.

Percent Anhydrous sodium soap (70:30 tallow-coconut oil) 75.2

Magnesium dodecyl benzene sulphonate 15 Miscellaneous ingredients (salt, glycerine, perfumes,

etc.) 1.8

Water to 100%.

were prepared by the following two processes.

EXAMPLE 2 COMPARATIVE EXAMPLE A A paste of magnesium dodecyl benzene sulphonate containing 50% of water was crutched with a soap base containing 30% of water, and the resulting mixture subjected to the same drying and tablet-forming techniques applied in the process of Example 2.

It was found that the drying stage of the process of Example 2 required 36.5% less steam than the corresponding stage of Example A.

EXAMPLES 3 AND 4 The soap tablets prepared in accordance with the invention were compared with a conventional superfatted soap tablet (B). The ingredients used to prepare these three soap tablets were as follows (expressed as percentages of the finished tablets):

Comparison of the in-use properties of these soap tablets produced the following results.

[(a) Rate of wear in water at 20 C. and 40 0.]

Weight loss (percent) 40 C. Example 20 C. 40 0. (wet) 3 26. 2 40. 2 48. 4 4 27.8 35.9 45.4 Comparative B 25.1 49. 6 47. 8

1 Between wear measurements the tablets were left in contact with a wet surface.

[(10) Loss of Weight due to mushing] Weight loss Example (g./50 cm 3"... 4. 8 4 4. 0 Comparative B. 4. 6

[(0) Volume of lather produced in water at 20 C. and 40 0.]

Lather volume (m1s.)

Example 20 C. 40 C.

3 828 1. 058 4 715 1, 033 Comparative B. 755 1, 020

[(d) Creamiuess of lather produced in water at 20 C. and 40 0.]

Creaminess score (0-5 scale) Example 20 C. 40 C.

3 3.6 3. 8 4 3. 4 3. 7 Comparative B- 3. 6 4. 3

All three types of soap tablet possessed excellent resistances to cracking and efiluorescence both during use and on drying out.

As can be seen from the above results, the tablets of Examples 3 and 4 had properties comparable with those of Comparative Example B, which comprised a much higher proportion of coconut oil soap.

What is claimed is:

1. A process for the preparation of a soap tablet, in which process:

(a) an aqueous alkali-metal soap base selected from the group consisting of sodium and potassium soap bases obtained by the saponification of tallow-class fats and nut oils, and mixtures thereof, said nut oils being those of which the fatty acid residues contain predominantly from 10 to 14 carbon atoms, and

(b) a substantially anhydrous slurry consisting essentially of an alkaline earth metal oxide selected from the group consisting of calcium oxide and magnesium oxide and mixtures thereof, and an alkyl benzene sulphonic acid selected from the group consisting of such acids wherein the alkyl chains contain from 8 to 22 carbon atoms and mixtures thereof, there being present in said slurry at least 2 moles of said sulphonic acid per mole of said metal oxide,

are admixed and subsequently formed into said soap tablet, the quantity of said slurry used being sufiicient to provide from about 5 to about 20% by weight in said soap tablet of alkaline earth metal alkyl benzene sulphonate detergent active material.

2. A process according to claim 1, in which said alkaline earth metal alkyl benzene sulphonate detergent active compound is used in an amount from about 5 to about 15% by Weight of said soap tablet.

3. A process according to claim 1, in which said alkyl aryl sulphonic acid is used in an amount of from about 1 to about 10% by weight of said soap tablet.

4. A process according to claim 1, in which said alkalimetal soap base is dried to a water content of from about 7 to about 13% by weight prior to being admixed with said slurry.

5. A process according to claim 4, in which said alkalimetal soap base is dried to a water content of from about 8 to about 10% by weight prior to being admixed with said slurry.

References Cited UNITED STATES PATENTS 3,150,097 9/1964 Kelly 252121 FOREIGN PATENTS 941,836 11/1963 Great Britain 252-121 736,279 8/1969 Belgium 252--121 HERBERT B. GUYNN, Primary Examiner U.S. Cl. X.R.

252l32, 370, 558, Dig. l6 

